net/hns3: simplify selecting Rx/Tx function

net/hns3: simplify selecting Rx/Tx function

Currently, there are four control variables (rx_simple_allowed,
rx_vec_allowed, tx_simple_allowed and tx_vec_allowed) which are used
to impact the selection of Rx/Tx burst function.

The purpose of the design is to provide a way to control the selection
of Rx/Tx burst function by modifying it's values, but these variables
have no entry to modify unless make intrusive modifications.

Now we already support runtime config to select Rx/Tx function, these
variables could be removed.

Fixes: a124f9e9591b ("net/hns3: add runtime config to select IO burst function")

Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>